Direct determination of vitamin C in fruit juices using a polyviologen-modified electrode

Abstract

A polyviologen-modified glassy carbon electrode (PV-GCE) was applied to directly determine vitamin C (i.e., ascorbic acid) in deeply colored, viscous, and turbid fruit juice samples. Compared to the results obtained at a bare GCE, the oxidation of vitamin C showed a large increase in current response at the PV-GCE in pH 4 buffer solutions. Preconcentration is the major factor for the signal enhancement. Square-wave voltammetry (SWV) was used for vitamin C detection at the PV-GCE. Under the optimized conditions, the SWV current signals showed a very wide linear range (up to 900 muM) with slope band regression coefficient of 0.051 muM muA(-1) and 0.998, respectively. The detection limit (S/N = 3) was 0.38 muM after 20 s of accumulation at open circuit. Since the content of vitamin C and pH value of most fruit juices are lower than 900 muM and close to pH 4, the determination can be done without dilution and other pretreatment of the samples. The results demonstrated a good precision and are in agreement with those obtained with other method.